1. Field of the Invention
The present invention is directed to a method for quantification and representation of in vivo fluid flow using data obtained in a magnetic resonance measurement sequence.
2. Description of the Prior Art
Using the phase contrast angiography, which is described in detail in the European Patent Specification 0 115 642, it is possible to quantitatively detect the flow in vessels with MR systems. The MR system has to meet high requirements in order to measure a sufficient spatial and time resolution of the flow in real time. When one wants to exactly measure the peak value, for example, of the systolic arterial blood flow in the human body, a time resolution under 40 ms is required. Additionally, the spacial resolution should at least be four times as large as the relevant vessel, which means so that one arrives at a required spatial, resolution of 2 mm for renal arteries, for example. A specific flow encoding with a changing flow encoding direction was suggested in the SMRM Abstracts Sydney 1998, page 2144 in order to realize the high spatial resolution in conjunction with the high time resolution given the phase contrast angiography. In this context, the conventional flow re-phasing can be foregone. Using EPI sequences, 27 flow coded images per second can be acquired with a spatial resolution of 2 mm, i.e. the above mentioned requirements can be met.
This known method has the disadvantage that even though a rapid measurement, ensues the evaluation is not carded out in real time. Thus, it is not possible to alter parameters of the intervention during the image data acquisition.
European Patent Specification 0 355 508 discloses a pulse sequence for measuring the time characteristic of a flow in a vessel by means of the magnetic resonance. A time resolution of the flow is carded out instead of a spatial resolution in one direction. However, neither the evaluation nor the display is carded out during the measuring process, so that this technique as well does not allow parameter modification during the measuring process.
Due to the lack of intervention capability, the measuring sequence must be completely restarted multiple times until the desired measuring result is finally obtained.
An object of the present invention is to provide a method for flow visualization using magnetic resonance imaging which can be used to guide an intervention in real time.
The above object is achieved in accordance with the principles of the present invention in a method for quantification of an in vivo fluid flow wherein a magnetic resonance scan of an object area is conducted using a magnetic resonance pulse sequence to obtain magnetic resonance signals from the object area. These magnetic resonance signals including signals representing in vivo fluid flow flowing at a flow rate, and wherein the magnetic resonance signals are phase-encoded dependent on the flow rate using a magnetic field gradient, and wherein the magnetic resonance signals are evaluated in real time and the flow rate, represented by the phase-encoding, is converted into a real time graphic display, and wherein, using the real time graphic display, parameters of the pulse sequence can be altered during the scan.
The applicability of the inventive method becomes, in general terms, as simple as an ultrasound Doppler measurement due to the interactive adjustability of parameters during the measuring process. However, the MR measurement has the important advantage that the measured slice can freely be chosen whereas ultrasound imaging has significant restrictions. Further, the direction of the flow sensitivity can be adjusted freely and independently of the chosen slice in an MR measurement, whereas the direction of the flow sensitivity always coincides with the slice direction in an ultrasound Doppler measurement.
In one embodiment, the rate dependent phase is color coded so that an image impression arises that is comparable to that of a color Doppler image obtained by ultrasound.